1. Field of the Invention
The present invention relates to combination read/write thin film magnetic heads used in floating-type magnetic heads and the like. In particular, the present invention relates to a combination read/write thin film magnetic head and a method for making the same, in which the track width of a magnetic gap of an inductive thin film magnetic head is highly precisely formed in order to reduce occurrence of write fringing.
2. Description of the Related Art
FIG. 14 is a longitudinal sectional-view of a conventional combination read/write thin film magnetic head, and FIG. 15 is a section facing a recording medium of the magnetic head shown in FIG. 14 and a fragmentary front view along arrow XV in FIG. 14. The magnetic head shown in FIGS. 14 and 15 is an inductive magnetic head which writes signals on a recording medium such as a hard disk. The inductive magnetic head is superposed with a reading head which uses the magnetoresistance effect at the trailing edge of the slider of a floating-type magnetic head which faces a recording medium such as a hard disk.
Identification number 11 in FIG. 14 represents a lower-core layer composed of a high magnetic permeability material such as a Fe-Ni alloy (permalloy). In a combination read/write thin film magnetic head in which an inductive head shown in FIG. 14 is continuously superposed with a reading head which uses the magnetoresistance effect, the lower-core layer 11 acts as an upper-shielding layer of the reading head.
A gap layer 12 composed of a nonmagnetic material such as Al.sub.2 O.sub.3 (aluminum oxide) is provided on the lower-core layer 11. An insulating layer 4 composed of an organic material, such as a resist material, is formed on the gap layer 12.
A coil layer 5 composed of an electrically conductive material having a low electric resistance, such as Cu, is spirally formed on the insulating layer 4. Herein, the coil layer 5 is formed so as to surround the periphery of the base end 7b of the upper-core layer 7, and a part of the coil layer 5 is shown in FIG. 14.
An insulating layer 6 composed of an organic resinous material is formed on the coil layer 5. An upper-core layer 7 composed of a magnetic material such as permalloy is formed by plating on the insulating layer 6. The front end 7a, facing the recording medium, of the upper-core layer 7 is jointed to the lower-core layer 11 through the gap layer 12. The base end 7b of the upper-core layer 7 is magnetically connected to the lower-core layer 11 through the holes formed in the gap layer 12 and the insulating layer 4.
In the inductive writing head, a recording current circulating in the coil layer 5 induces a recording magnetic field in the lower-core layer 11 and the upper-core layer 7, and magnetic signals are recorded on a recording medium such as a hard disk by means of a leakage magnetic field from the magnetic gap between the lower-core layer 11 and the front end 7a of the upper-core layer 7.
In the magnetic gap for the inductive writing head, the gap length G1 is determined by the distance between the lower-core layer 11 and the front end 7a of the upper-core layer 7 which are jointed through the gap layer 12, i.e., the thickness of the gap layer 12, and the gap depth Gd is determined by the depth at the front end 7a of the upper-core layer 7. Further, the track width Tw is determined by a width of the front end 7a of the upper-core layer 7, as shown in FIG. 15.
As shown in FIG. 15, the width T3 of the lower-core layer 11 is sufficiently larger than the width of the front end 7a of the upper-core layer 7, because the lower-core layer 11 has magnetic shield effects to a magnetoresistive element 13 which is formed below the inductive head. That is, in a reading head which uses the magnetoresistance effect as shown in FIG. 15, the magnetoresistive element 13 is provided on a lower-shielding layer 14 through the lower-gap layer 15a and the lower-core layer 11 is formed on the magnetoresistive element 13 through the upper-gap layer. The lower-core layer 11 also acts as the upper-shielding layer to the magnetoresistive element 13. The width T3 of the lower-core layer 11 therefore is sufficiently larger than the width of the magnetoresistive element 13 in order to achieve the function as the upper-shielding layer.
As shown in FIG. 15, a width T3 of the lower-core layer 11 larger than the width Tw of the front end 7a of the upper-core layer 7 induces a recording magnetic field in the lower-core layer 11 and the upper-core layer 7, and a leakage magnetic field formed between the front end 7a and the lower-core layer 11 leaks out of the track width Tw. A leakage magnetic field is also formed beside both sides of the track width Tw due to a large width of the lower-core layer 11.
As a result, the magnetic signals formed on the recording surface of a recording medium such as a hard disk has write fringing or writing blot of magnetic signals which is formed out of the given width Tw of the recording track. The write fringing inhibits high precision detection of the track position in the written recording medium and results in tracking servo errors. In particular, the write fringing significantly affects high density recording with a narrow track pitch.
FIG. 16A is a front view from the recording medium side of an improved head which can suppress the write fringing. In FIG. 16A, after a gap layer 12 is formed on the lower-core layer 11 and a front end 7a of an upper-core layer 7 is formed on the gap layer 12, the lower-core layer 11 and the gap layer 12 are removed by ion milling or the like to form grades 11a and 12a over the lower-core layer 11 and the gap layer 12 at both edges of the front end 7a of the upper-core layer 7. Both of the grades 11a and 12a have an angle .theta..sub.5.
Because the grades 12a are simultaneously formed over both ends of the gap layer 12 by the ion-milling process for forming the lower-core layer 11 and the gap layer 12, the width T6 of the face 11b of the lower-core layer 11 facing the front end 7a is larger than the width Tw of the front end 7a. FIG. 16B represents a recording pattern of magnetic data recorded with this head. Since the width T6 of the face 11b is larger than the width Tw, the writing magnetic field leaks out of the track width Tw at the right and left ends to form write fringing.
The head shown in FIG. 16A can reduce write fringing compared to that shown in FIG. 15. A finer track pitch for high density recording will cause some detecting errors due to the write fringing shown in FIG. 16B, and thus the improvement shown in the drawing will be insufficient.